1. Field of the Invention
The present invention relates to a tool life control method for detecting an expiration of the tool life of a machine tool, and more particularly, to a tool life control method based on a disturbance load estimation.
2. Description of the Related Art
When a machine tool is used for a long period of time, the tool progressively wears out, which deteriorates its cutting capability. It is necessary, therefore, to manage the tools in use so that an exhausted tool is replaced with a new tool. Conventionally, a tool life control is performed by observing the tool itself or a condition of the cut workpiece to see if the tool is worn out. Japanese Patent Laid-Open Publication No. 1-183338 is directed to a method of tool management in which the working hours of individual tools are integrated and when the integrated working hours of the tool reaches a predetermined lifetime, the tool is replaced.
In another conventional tool management method, the wear of the tool is measured by visually observing the tool or the condition of the cut workpiece. In this case, it depends on the experience and intuition of the person in charge of the tool management to determine the time for a tool change. This method lacks accuracy and has no objective criterion for the tool management. Moreover, according to the aforesaid tool management method in which the working hours of each tool is integrated and the tool is changed when the predetermined lifetime is reached by the integrated time, a tool may be replaced as an exhausted tool even if actual wear of the tool is so small that the tool is not yet exhausted. On the other hand, even though the actual tool wear is so large that the time for a tool change is reached, the tool may fail to be changed since the .lifetime is not reached by the working time. This method, therefore, involves the problems such as the deterioration of the machining accuracy and the waste of energy and time. Thus, this tool life control based on the working time is not an accurate and absolute method of tool life control.